The present invention relates generally to data communication networks and, more particularly, to a low-cost asynchronous transfer mode subnetwork suitable for applications in a home environment.
Asynchronous Transfer Mode (xe2x80x9cATMxe2x80x9d) is an emerging packet switching network technology designed to provide service for a wide variety of applications such as voice, video and data. Originally proposed for use in the Broadband Integrated Services Digital Network (xe2x80x9cB-ISDNxe2x80x9d) by the International Telegraph and Telephone Consultative Committee (xe2x80x9cCCITTxe2x80x9d), now reorganized as the Telecommunications Standardization Sector of the International Telecommunication Union (xe2x80x9cITU-Txe2x80x9d), ATM has moved beyond the wide area network setting into the private network arena as a platform for local area networks (xe2x80x9cLANsxe2x80x9d) with multimedia capabilities. ATM is now well known in the art and is described in various references. See e.g., Martin de Prycker, Asynchronous Transfer Mode: Solution for Broadband ISDN (2nd Ed., Ellis Horwood Ltd., West Sussex, England, 1993).
In an ATM network, as defined by the CCITT standards, information is carried in packets of fixed size, specified for B-ISDN as 53 bytes or octets, called cells. These cells are individually labelled by addressing information contained in the first 5 bytes (octets) of each cell. Although ATM evolved from Time Division Multiplexing concepts, cells from multiple sources are statistically multiplexed into a single transmission facility. Cells are identified by the contents of their headers rather than by their time position in the multiplexed stream. A single ATM transmission facility may carry hundreds of thousands of ATM cells per second originating from a multiplicity of sources and travelling to a multiplicity of destinations.
ATM is a connection-oriented technology. Rather than broadcasting cells onto a shared wire or fiber for all network members to receive, a specific routing path through the network, called a virtual circuit, is set up between two end nodes before any data is transmitted. Cells identified with a particular virtual circuit are only delivered to nodes on that virtual circuit and are guaranteed to arrive at their destination in the transmitted order. ATM also defines virtual paths, bundles of virtual circuits traveling together through at least a portion of the network, the use of which can simplify network management.
The backbone of an ATM network includes switching devices capable of handling the high-speed ATM cell streams. Switching components of these devices perform the functions required to implement a virtual circuit by receiving ATM cells from an input port, analyzing the information in the header of the incoming cells in real-time, and routing them to the appropriate destination port.
An ATM network makes no guarantees that it will deliver each and every packet to its intended destination. Rather, ATM provides the capability of offering multiple grades of service in support of various forms of traffic requiring different levels of cell loss probability and propagation delay. It is known, for instance, that many multimedia connections, e.g., video streams, can tolerate relatively large cell losses, but are very sensitive to delay variations from one cell to the next. In contrast, traditional forms of data traffic are more tolerant of large propagation delays and delay variance, but require very low cell losses. Because of this ability to handle diverse data streams, ATM is an ideal platform for network configurations supporting both multimedia and conventional data transmission.
Applications such as video-conferencing or virtual reality have driven the deployment of ATM into the LAN setting. Simultaneously, a number of new applications directed at residential consumers have been proposed, such as video-on-demand (xe2x80x9cVODxe2x80x9d), home theater, interactive television and multi-room stereo sound systems. The multimedia nature of these applications have led researchers to investigate the concept of a xe2x80x9chome area networkxe2x80x9d (xe2x80x9cHANxe2x80x9d) capable of supporting these services. Indeed, the advent of a new wall socket in the home which gives wide area access at reasonable bandwidth, even though it will only be used initially for VOD applications, is an important seed towards establishing data outlets in every room in the house. In effect, this model tracks the deployment of residential telephone service over the last half century. This installed wiring could form the physical backbone of a HAN, and ATM, being well suited for multimedia applications, would be a logical choice as a network platform. However, for ATM technology to dominate a future HAN market, there must be more seeding routes which will introduce a diversity of ATM devices within the home.
One method for introducing ATM into the HAN field is to replace existing point-to-point interconnection systems with point-to-point ATM. SP-DIF, the digital interconnect for sound systems found on compact disc (xe2x80x9cCDxe2x80x9d) and digital audio tape (xe2x80x9cDATxe2x80x9d) players and home theater products is a prime candidate. While the savings in component cost in moving from an SP-DIF implementation to an ATM implementation is arguable, the ATM version has the benefit that a switch can be inserted in series with a link to enable streams to be freely switched and routed.
This use of ATM could further enhance convergence of existing technologies. In the home, televisions have converged with stereo sound system components and will converge with multi-room sound systems and home theater components. Since all these devices may be implemented using ATM, there is a potential for new applications which integrate these components in various ways. For example, stereo speakers may be used for personal computer (xe2x80x9cPCxe2x80x9d) sound output or a PC monitor may be employed to index a video or CD collection. Further, other home electronic components such as baby monitors, doorbells, heat control, and security components could be added to an ATM HAN. In fact, integration of these devices would enable sharing to reduce the total number of needed peripherals and processors. Instead of requiring separate loudspeakers in the answering machine, the television, the stereo HiFi, the doorbell and the baby monitor, one set of loudspeakers could be shared by these devices. This feature would have obvious benefit for people who frequently use headphones.
The provision of a wide-area connection to the home, used in conjunction with an ATM HAN, could enable the user to remotely answer the front door of the home, to check home security or monitor and control devices within the home. Similarly, an ATM HAN could facilitate remote meter reading for utilities, or even collection of television viewing rating information. As further examples, an ATM HAN could be used, in a class of protected housing for the elderly, to monitor room temperature and general activity as it is done today over the telephone system. In fact, a few mainstream ATM seeds, such as VOD, could spawn many similar applications.
Although it is apparent that an ATM HAN could yield many conceivable benefits, the technology to practically implement an ATM HAN has not previously existed. Some prior systems, mainly VOD trials, do exist which deploy ATM technology to the home in a minimal way. These systems, employed in early VOD trials, use ATM in the core of the network, but terminate ATM Adaption Layer Type 1 (xe2x80x9cAAL1xe2x80x9d) circuit emulation before entry into the home. Instead, the home is fed with a fairly inflexible structure, such as a continuous MPEG multiplex transport stream. Although this is still one of the options recognized by the Digital Audio Visual Counsel, or DAVIC, it does not support multiple streams to the home or permit communication between devices within the home. Nor does the system support any sizable bandwidth out of the home.
A more sophisticated system was employed in the Cambridge Interactive Television (xe2x80x9ciTVxe2x80x9d) Trial. See Geoff Vincent, The Cambridge ITV Trial, Online Media (1995). The system used in the Cambridge iTV Trial offers each home an ATM Forum compliant User Network Interface (xe2x80x9cUNIxe2x80x9d) which can either be directly connected to a home set top box (xe2x80x9cSTBxe2x80x9d), or connected to a consumer ATM switch. Being a UNI-compliant system, the cell format, traffic contract, signalling, and operations and maintenance procedures defined by the ATM Forum are followed. See G. Ratta, ATM Forum User-Network Interface Specification, Version 3.1 (ATM Forum publication, September 1994). Thus, any vendor""s current generation ATM equipment can, in principle, be installed in a network within the home.
Although the Cambridge iTV Trial system theoretically provides capability of creating a HAN with a wide area access point, such a network would be far too costly to be deployed in the residential setting. Unfortunately, the switching devices and current interfaces required for ATM networks, including the Cambridge iTV system, make the use of these networks within the home prohibitively expensive. The major problem lies with current ATM protocols which require that the switches and end stations support vast quantities of signalling and management software, including a base set consisting of Q.2931, SSCOP, and SNMP. For a large class of possible simple ATM devices, such as those described above, the memory and processors required to implement these protocols is more expensive than the sum of the cost of the actual data handling components. Conceivably, lightweight versions of these protocols could be developed which would reduce the processing power necessary to implement simpler ATM switches and interfaces. However, even these protocols would require a minimum of software support which would be too costly for a large class of applications. Indeed, many devices could not be cost-effectively integrated into an ATM network unless fully-hardware switches and interfaces could be employed.
Therefore, a need persists for a reliable, yet low-cost, ATM HAN. Such a network would provide the service capability of conventional ATM networks and be able to support the full panoply of emerging multimedia applications for the home, but be inexpensive enough to be installed in residential environments.
In general, it is an object of the invention to provide a subnetwork using asynchronous transfer mode which has the advantage of meeting the requirements of emerging multimedia applications at a low cost.
It is a further object of the invention to decrease the cost of the subnetwork by controlling the subnetwork with external computer means to enable the use of inexpensive, simple ATM devices and switches.
It is a further object of the invention to allow the user to attach any device to any location in the subnetwork without manually configuring the subnetwork with unique identifiers for each device.
It is a further object of the invention to automate the determination of a spanning tree in the network which will be used to communicate control information.
These and other objectives are achieved by an ATM subnetwork comprising at least one end station communicating with at least one switch through at least one multi-access bus, where end stations and switches form an interconnected mesh, and a controller connected to the interconnected mesh for managing virtual circuits in the interconnected mesh which transport data between the end stations. The controller is external to the interconnected mesh and is connected to the interconnected mesh at a single control point, and may be optionally further connected to a conventional ATM network. The bus of the subnetwork is either bidirectional or unidirectional and functions as a distributed switch in the subnetwork.
The controller acts as a proxy for the switches within the interconnected mesh such that the signalling and management functions typically required by ATM protocols are performed by the controller, rather than the individual switches. Separate proxy controllers perform a similar function for the end stations, and proxy signalling agents permit standard ATM devices to connect to the switches. This off-loading of software to computers outside the interconnected mesh permits the switches and end stations to be implemented in low-cost full-hardware configurations.
The controller achieves this proxy control by communicating with switches via a control protocol. Each switch has an internal control address space accessible by the controller using the control protocol. The control protocol comprises single cell messages which enable the controller to read and write to locations within a switch""s control address space. Each switch and end station has a unique network address defined by the topology of the interconnection of the switch relative to the single control point. This address comprises the concatenated sequence of switch port numbers forming the route through the interconnected mesh from the single control point to the switch, where the route is confined to a spanning tree superimposed on the interconnected mesh and rooted at the single control point. The controller presides over a distributed topology determination algorithm which determines this spanning tree.
Data originating from the conventional ATM network is presented to the interconnected mesh at the single control point. It is possible to connect other conventional ATM networks at points other than the single control point since the system uses switch proxies. This external point of connection may serve as a boundary of ownership and physical access. In particular, processes related to security, encryption, policing and authentication can be inserted at this place and implementation of these procedures is then shared over all devices and switches connected to each other.
In accordance with another aspect of the invention, a method for managing communications in a subnetwork using asynchronous transfer mode comprises the steps of interconnecting end stations and switches to form an interconnected mesh, presenting data to the interconnected mesh at a point of entry to the interconnected mesh, controlling the interconnected mesh by a proxy connected to the interconnected mesh, and determining, by the proxy, virtual circuits in the interconnected mesh for routing the data to and between the end stations.
In accordance with another aspect of the invention, a method for determining a spanning tree of a network, the network having at least one switch and the switch having a plurality of ports, comprises the steps of sending, by each switch, a plurality of register commands, one register command being sent on each of the plurality of ports of the switch, receiving the plurality of register commands by a controller, selecting one of the received register commands, acknowledging the switch identified by the selected register command, and including the identified switch in the spanning tree of the network. The acknowledging step comprises sending a acknowledgement message to the identified switch. The method further comprises the step of propagating towards the controller, by a previously acknowledged switch, each register command received by that switch.